I wouldn't use 100LL, especially in a high compression, direct injection engine. Pressures and heat are already considerable in those. 100LL runs pretty hot. Aircraft engines are typically low compression. When I was a pilot and was constantly around airports I used to fill up my bikes and old mustangs with 100LL. One of my bikes designed to be run on leaded gas would have a small gasket leak anytime I used unleaded. When it had avgas in it, it wouldn't have the leak at all. Just as engines that were designed to use leaded gas started having problems with unleaded fuels, mainly valve seating problems, the engines designed to have unleaded fuel could have problems using low lead.

They now have to design engines not only to run on unleaded gas, but it is absolute crap. Ethanol mixtures determined by regional and state laws has only made gas worse over the years. Ethanol is a horrible product which turns foamy and nasty in a car. Left in a tank it will accumulate water and ruin old metal tanks. It gunks injectors and decreases fuel efficiency. feel good naer- do- wells think they are doing good for the environment, but in reality the offset of decreased efficiency thus increase in fuel consumption only increases pollutants in the end. End of rant.

Well I'm just curious, I know some people run 100 octane UL racing fuel and was wondering if it would have problems with leaded fuel or not. I run 100LL in my 1960 Chrysler Windsor because it was made for leaded, but I wouldn't try it in a UL engine without doing some research first.

That seems to sum it up nicely. 100 unleaded would be a waste and 100LL would not only be a waste, but it would cause additional fouling especially in a high compression direct injection engine most especially when they already have carbon issues.

As a side note those of us who ran the old 60's muscle cars designed for leaded fuel after they made the switch used to use a product called marvel mystery oil. I have no idea if it is still made, but I would imagine it is. We mixed a cap of it into each gallon pumped and it would lubricate the valves and keep from having the seating problem. I used it in my old cars, old BMW and Harley bikes. You couldn't keep a harley from leaking oil, but at east you could keep the valves from sticking or leaking.

I happen to work around that stuff as I am a G.S.E. mechanic. The line service guys keep putting sump fuel 100LL in the tugs and other gas powered equipment ant it fowls the plugs really badly in short time. This one kid put about 2 gallons into a nearly full tank in his 91 Toyota pickup and plugged the cat in less than a day. Bad stuff for cats...

I happen to work around that stuff as I am a G.S.E. mechanic. The line service guys keep putting sump fuel 100LL in the tugs and other gas powered equipment ant it fowls the plugs really badly in short time. This one kid put about 2 gallons into a nearly full tank in his 91 Toyota pickup and plugged the cat in less than a day. Bad stuff for cats...